EBV transformation and human-human hybridoma formation will be used to establish continuous B cell lines secreting human monoclonal antibodies (HMAs) to HTLV-III envelope antigens by immortalization of antigen-specific B cells from infected patients. B cell cultures initiated in each experiment will be screened for antibodies reacting with the HTLV-III strain previously isolated from the B cell donor. Antigens to which HMAs bind will be characterized by standard immunochemical methods. These HMAs will be potent tools for determining to what extent antigenic variation, which is predicted from the genomic polymorphism of HTLV-III within the env gene, but thus far not demonstrated serologically, occurs among virus strains isolated from different patients. Using a battery of HMAs to conserved and variant antigens, it will be possible to look for evidence of antigenic drift in sequential isolates of HTLV-III from the same patient. These HMAs will also be applied to study the topologic arrangement of epitopes on viral envelope glycoproteins and the results of these studies will be correlated with studies to determine which epitopes are responsible for virus attachment to the T4 molecule, for syncytia formation, and for inducing neutralizing antibodies. The capacity of HMAs to inhibit viral functions will also be correlated with the subclass and avidity of each antibody. Mechanisms that may explain the apparently poor neutralizing activity of antibodies in patient sera will also be investigated.